The present invention relates generally to power and drive systems employing a three-phase bridge inverter operated by a rechargable DC source to supply AC power to operate a polyphase load. More particularly, the invention is concerned with an integrated traction inverter and battery charger apparatus capable of operating in either a drive mode to operate the polyphase load or a charge mode to recharge the DC source.
Compared to a DC brush-type motor, it is more advantageous to use a three-phase motor (e.g., induction, DC brushless and switched reluctance) in many applications, such as electrically powered vehicles, load leveling systems, standby AC power systems and uninterruptible power systems. While the DC brush-type motor is simpler to supply with power for operation, its construction has drawbacks. This DC motor has a mechanical commutator and brushes which contact while moving relative to one another. Thus, these components are subject to wear and must be given periodic maintenance.
These drawbacks are eliminated in the construction of a three-phase motor. It has a simplier, brushless construction and therefore is highly reliable and requires relatively low maintenance. For these reasons it can be operated at higher speeds than a brush-type motor and hence has increased power to volume and weight ratio.
These advantages make the three-phase brushless motor more attractive than the brush-type motor even though the brushless motor requires a more complex device to supply power to it from a DC battery. Whereas the brush-type motor requires a relatively simple DC-to-DC converter to power it, the three-phase brushless motor requires a relatively more complex three-phase bridge inverter to generate the rotating magnetic field which operates the motor.
Notwithstanding the advantages of using a three-phase motor for many applications, in vehicular traction drive systems the complexity it adds raises other problems. Typically, both the DC battery operated three-phase bridge inverter and a single-phase boost-regulated battery charger are mounted onboard the vehicle with the AC traction motor. The complexity of these components oftentimes makes it difficult to minimize or reduce their weight and the space they take up on the vehicle which correspondingly affects adversely the overall performance and desirability of the drive system employing the three-phase motor. Consequently, a need exists for improvements which will alleviate these problems.